Southern Ontario: Thunderstorm Outlook for Sunday, August 1, 2021

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Forecast Discussion

Pop-up thunderstorms are possible throughout much of Southern Ontario during the afternoon and evening on Sunday. For the most part, these storms should remain non-severe although there is a very low questionable risk for some marginally severe storms mainly around the Lake Ontario shoreline and into parts of Central Ontario near Lake Simcoe. The main risks will include some strong wind gusts, moderate-sized hail and intense downpours that may lead to localized flooding. We should see the storm risk come to an end by the late evening as the storms move south and east of the border over Upstate New York.

Southern Ontario: Thunderstorm Outlook for Saturday, July 31, 2021

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Forecast Discussion

There is the potential for an isolated non-severe thunderstorm around Lake Huron and Georgian Bay, but at this time the risk isn’t focused on a particular area so a forecast is not being issued. The best chance for storms is later in the evening and overnight into Sunday morning.

Northern Ontario: Thunderstorm Outlook for Friday, July 30, 2021

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Forecast Discussion

A few scattered thunderstorms may develop during the afternoon and evening on Friday through Northwestern Ontario along the Manitoba border. There is some questionable severe risk associated with these storms with the main threats including damaging wind gusts and large hail. While not the main risk, there are some indications that an isolated tornado could be possible especially around Drayden and Red Lake. The tornado risk isn’t strong enough for us to include it in the forecast map at this point. We’ll see the storm threat come to an end late in the evening as the storms head stateside to the southeast.

Southern Ontario: Thunderstorm Outlook for Thursday, July 29, 2021

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Forecast Discussion

An area of quite intense storms has developed over Wisconsin late Wednesday evening and the current cluster of isolated storms is expected to organize into a line with embedded thunderstorms that could bring destructive wind gusts later tonight. This complex will make its way across Michigan just after midnight and could reach Southwestern Ontario by the early morning hours.

There is some uncertainty in exactly how strong this line will be by the time it crosses into our region, but it’s possible that the environment might be strong enough to sustain a damaging wind gust risk well into the morning. One or two tornadoes can’t be ruled out although it’s questionable as the better tornado risk is will into Michigan and over Wisconsin. Small to moderate size hail could also be an issue, but unlikely to see anything too large.

Considering that many are sleeping during the time when the worst conditions are expected, it’s highly recommended that residents in the risk area have a way to receive storm updates. Be ready to seek shelter if necessary. Tornadoes at night can be particularly dangerous at night because they’re hard to see due to the lack of light.

Some localized non-severe storms are expected throughout all of Southern Ontario later in the day on Thursday. At this point, it appears that the severe risk with any of these storms is pretty low. Should remain non-severe for the most part. The storm risk will come to an end later in the evening.

Northern Ontario: Thunderstorm Outlook for Wednesday, July 28, 2021

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Forecast Discussion

There is the potential for thunderstorms throughout much of Northern Ontario during the day on Wednesday. It will begin with a few non-severe storms for parts of Northwestern Ontario during the morning with more storms expected to develop later in the day. Some of these afternoon and evening storms could reach severe levels mainly in Northwestern Ontario with large hail, strong wind gusts and heavy rainfall. The threat will come to an end late in the evening as the severe storms move stateside. Non-severe storms may continue through the overnight into Thursday morning for Northeastern Ontario.

Southern Ontario: Thunderstorm Outlook for Tuesday, July 27, 2021

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Forecast Discussion

Two waves of thunderstorms will sweep across Southern Ontario on Tuesday with the first round coming during the morning with some isolated non-severe thunderstorms for Central, Southwestern and Eastern Ontario. Later in the day on Tuesday, there is a questionable risk of some pop-up thunderstorms during the afternoon and early evening mainly through Southwestern Ontario and parts of Central/Eastern Ontario. The storms in Southwestern Ontario have the potential to become severe with large hail, damaging wind gusts and heavy rainfall. Now, this isn’t guaranteed and is heavily dependent on if storms actually develop to take advantage of the environment. Storms will weaken late in the evening as they move out of the region.

Northern Ontario: Thunderstorm Outlook for Sunday, July 25, 2021

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Forecast Discussion

Scattered non-severe thunderstorms are possible across parts of Northern Ontario during the afternoon and evening on Sunday stretching from Sandy Lake and eastward towards Cochrane and Moosonee. These storms will have the typical risk associated with them including small hail, strong wind gusts and heavy rainfall. The storm threat will come to an end by late evening.

Southern Ontario: Thunderstorm Outlook for Saturday, July 24, 2021

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MAP UPDATED - July 24 @ 2 PM

MAP UPDATED - July 24 @ 2 PM

UPDATE (July 24 - 2:00 PM)

We haven't changed much from our forecast that we posted late last night. Although we have expanded the orange (severe risk) zone further to the northeast to include the Owen Sound and Meaford area. The environment is stronger than we expected in that area so that was enough to merit an upgrade.

Another minor change is expanding the tornado risk zone around the Georgian Bay shoreline so it extends further inland through parts of Muskoka and Simcoe County. The tornado risk isn't super strong here, but it can't be ruled out if a few storms pop up.

The main concern with regards to tornadoes is around the Lake Huron shoreline from Kincardine to Grand Bend. We're constantly seeing this area highlighted in the data for some quite intense storms and the environment is very favourable for one or two tornadoes. If you live near Lake Huron, you should have a plan in place to seek shelter if the tornado potential actually materializes over the next few hours.

Already seeing some storm development over Michigan and this will likely further intensify as it tracks to the west and towards Southwestern Ontario later this afternoon. It looks like the late afternoon and early evening will be when we should see the strongest severe threat although the storm risk may linger well after sunset - a nocturnal tornado can't be ruled out so it's extremely important you stay weather aware today.

Outside of the tornado threat, these storms could bring the potential for large hail and especially widespread wind damage. Another concern will be the heavy rainfall associated with all the storm activity. Some regions particularly around the northeast and eastern shoreline of Georgian Bay could see between 50-100mm by the end of the day. So flash flooding could be a huge issue considering many of these locations have already seen a lot of rain over the past few weeks.

Old Forecast Discussion

A rainy and stormy start to the weekend is expected across parts of Southern Ontario with the risk of some severe thunderstorms during the afternoon and evening on Saturday. Exactly how strong this risk will be is still a little questionable as timing could make or break the storm threat. Current model data show a line of precipitation with embedded thunderstorms sweeping through Southern Ontario during the afternoon on Saturday which could pose an isolated severe threat, but the main risk will come later in the day with a potential second round of storms.

Where this second round of storms initiates will be key in what threat they will pose to our region. If that first line of precipitation is earlier than expected this will allow enough time for the environment to build and support storm development later in the day. On the other hand, if the line moves through later in the day it’ll mean that storms initiate over Michigan and will be quite weak by the time to cross over Lake Huron late in the evening.

IF (and that’s a big if) the second round of storms develop and reach our region early enough we could see the potential for large hail, damaging wind gusts and maybe even one or two tornadoes with the highest chance along the Lake Huron shoreline and down into Deep Southwestern Ontario. If these storms hold off until later in the evening then the focus will shift towards mainly a damaging wind risk as the cluster of mature storms track to the east during the overnight hours. This risk may stretch into areas to the east of Georgian Bay as well with some indication of a few isolated cells developing over Georgian Bay.

The further east you go the lower the storm threat as the strongest activity will be mostly focused on the western part of our region. The Ottawa Valley will likely not see much activity until maybe Sunday morning as the storms from Saturday evening reaches that area, but they’ll be much weaker and well below severe levels

We’ll continue to monitor the latest data and issue a final forecast by Saturday early afternoon if required.